Light-emitting device and lighting apparatus incorporating same

ABSTRACT

A light-emitting device is provided that can extract light in all directions and that has wide directivity. This light-emitting device includes: an elongated bar-shaped package extending sideways, the package being formed such that a plurality of leads are formed integrally with a first resin with part of the leads exposed; a light-emitting element that is fixed onto at least one of the leads and that is electrically connected to at least one of the leads; and a second resin sealing the light-emitting element. In the light-emitting device, the first resin and the second resin are formed of optically transparent resin, and the leads have outer lead portions used for external connection and protruding sideways from both left and right ends of the package.

This application is based on Japanese Patent Application No. 2008-008899filed on Jan. 18, 2008, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device and a lightingapparatus incorporating such a light-emitting device, and moreparticularly to a light-emitting device provided with a light-emittingelement and a lighting apparatus incorporating such a light-emittingdevice.

2. Description of Related Art

In JP-A-2003-168824, there is disclosed a structure in which alight-emitting element and a resin for sealing the light-emittingelement are provided in the reflective frame of a package. A lead frameis employed as the package, and the reflective frame is formed of whiteresin. Since the structure includes the reflective frame as describedabove, light emitted from the light-emitting element is extracted withincreased directivity in one direction.

In JP-T-2003-519929, there is disclosed a structure in which alight-emitting element is sealed with a resin containing fluorescentmaterial without the use of a reflective frame.

The structure of the reflective frame disclosed in JP-A-2003-168824 isnot suitable to diffuse light in all directions. In the structuredisclosed in JP-T-2003-519929 and having no reflective frame, since asealing resin is molded at one time, it is difficult to design thedetailed shape of the resin. In particular, when a fluorescent materialor a light diffusing material is contained in the resin, it is difficultto place the contained material in an optimum position due to therelationship between the specific gravities of the resin and thecontained material. In the structures disclosed in JP-A-2003-168824 andJP-T-2003-519929, both their overall shapes are substantiallybox-shaped; the structures are of a terminal intended for surfacemounting on a circuit board. Thus, they are not suitable as analternative to a linear light source placed in the air like a metalfilament.

SUMMARY OF THE INVENTION

To overcome the foregoing advantage, it is an object of the presentinvention to provide a light-emitting device suitable as an alternativeto a linear light source that is placed in the air like a filament and alighting apparatus incorporating such a light-emitting device. It isanother object of the invention to provide a light-emitting device thatdecreases light directivity and that easily extracts light in alldirections.

A light-emitting device according to a first aspect of the presentinvention includes: an elongated bar-shaped package extending sideways,the package being formed such that a plurality of leads are formedintegrally with a first resin with part of the leads exposed; alight-emitting element that is fixed onto at least one of the leads andthat is electrically connected to at least one of the leads; and asecond resin sealing the light-emitting element. In the light-emittingdevice, the first resin and the second resin are formed of opticallytransparent resin, and the leads have outer lead portions used forexternal connection and protruding sideways from both left and rightends of the package.

With the light-emitting device of the first aspect of the invention,since, as described above, the first and second resins are formed ofoptically transparent resin, it is possible to make both the resinsfunction as light guiding members. Thus, it is possible to guide lighttoward the back side of the lead on which light-emitting diodes arearranged. Since the bar-shaped package is used, linear light can begenerated. Moreover, since outer lead portions used for externalconnection protrude sideways from both left and right ends of thepackage, it is possible to increase workability when adjacent ones ofthe light-emitting device are firmly attached such as by welding.

In the light-emitting device of the first aspect of the invention, thesecond resin may include fluorescent material. Thus, it is possible tochange the color of light emitted from the light-emitting device withthe fluorescent material included in the second resin.

A lighting apparatus according to a second aspect of the inventionincludes: a plurality of the light-emitting devices of the first aspect;a filament including the light-emitting devices; and power supply leadselectrically connected to the filament. In the lighting apparatus, thefilament is so configured that adjacent ones of outer lead portions arefirmly attached and connected in series such that adjacent ones of thelight-emitting devices are V-shaped, and both ends of the outer leadportions connected in series are firmly attached to the power supplyleads.

Since, in the lighting apparatus of the second aspect of the invention,as described above, adjacent ones of the outer lead portions are firmlyattached and connected in series such that adjacent ones of thebar-shaped light-emitting devices are V-shaped, the lighting apparatuscan take the same form of light emission as a metal filament. Moreover,since the bar-shaped light-emitting devices are formed of opticallytransparent resin, it is possible to provide a lighting apparatus thatcan extract light not only in directions toward the front and back ofthe leads but also in directions in which the outer lead portions usedfor external connection extend and that evenly emits light 360 degrees,that is, in all directions.

As described above, according to the present invention, it is possibleto provide light-emitting devices that can extract light over a widearea and that have wide directivity and a lighting apparatusincorporating such light-emitting devices. It is also possible toprovide light-emitting devices in which adjacent ones of thelight-emitting devices are firmly attached with ease.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view taken along a lengthwise direction of alight-emitting device according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view taken along a widthwise direction ofthe light-emitting device according to the embodiment of the invention;

FIG. 3A is a diagram showing a process of fabricating the light-emittingdevice according to the embodiment of the invention;

FIG. 3B is another diagram showing the process of fabricating thelight-emitting device according to the embodiment of the invention;

FIG. 3C is another diagram showing the process of fabricating thelight-emitting device according to the embodiment of the invention;

FIG. 3D is another diagram showing the process of fabricating thelight-emitting device according to the embodiment of the invention;

FIG. 4A shows the directional characteristics of the light-emittingdevice according to the embodiment of the invention;

FIG. 4B shows the directional characteristics of an example of aconventional light-emitting device;

FIG. 5 is a cross-sectional view taken along a widthwise direction of alight-emitting device according to another embodiment of the invention;

FIG. 6 is a cross-sectional view taken along a widthwise direction of alight-emitting device according to yet another embodiment of theinvention; and

FIG. 7 is a front view of a light bulb according to still yet anotherembodiment of the invention, with its glass cover omitted.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the accompanying drawings. FIG. 1 is a cross-sectional viewtaken along a lengthwise direction of a light-emitting device accordingto an embodiment of the invention. FIG. 2 is a cross-sectional viewtaken along a widthwise direction of the light-emitting device accordingto the embodiment of the invention. FIG. 1 shows the cross-sectionalview taken along line A-A of FIG. 3D; FIG. 2 shows a cross-sectionalview taken along line B-B of FIG. 3D.

A light-emitting device 1 is configured such that light-emittingelements 3 are incorporated in a lead-frame type package 2, that theselight-emitting elements 3 are sealed with resin and that thelight-emitting device 1 is formed overall in the shape of an elongatedbar. The package 2 is formed in the shape of an elongated bar extendingsideways such that parts of a plurality of leads 41, 42 and 43 formedwith a lead frame 4 are exposed and that the leads 41, 42 and 43 areformed integrally with a first resin 5. The light-emitting elements 3are fixed on at least one of the leads 41, 42 and 43 with adhesivematerial. The light-emitting elements 3 are electrically connected to atleast one of the leads 41, 42 and 43 by bonding wires 6. In thisembodiment, a lead on which the light-emitting elements are fixed iswired, by bonding wires 6, to the other leads adjacent to the leadmentioned previously. Although the above description discusses the casewhere the number of light-emitting elements incorporated in the packageis two, the number of light-emitting elements is not limited to thisnumber. The number of light-emitting elements is arbitrarily determinedaccording to the shape of the light-emitting device 1. Thelight-emitting elements 3 incorporated in the package 2 are sealed witha second resin 7 different from the first resin 5. As the light-emittingelements 3, light-emitting elements composed of, for example,light-emitting diodes can be used.

A method of fabricating the light-emitting device 1 will be describedbelow in detail with reference to a fabrication process shown in FIGS.3A to 3D.

First, as shown in FIG. 3A, the lead frame in which a plurality of leads41, 42 and 43 are connected by tie bars 44 is prepared. This lead frameis formed of metal material such as iron-based material or copper-basedmaterial. The leads 41, 42 and 43 are connected to a main frame (notshown) through the tie bars 44. Although the leads for onelight-emitting device 1 are only shown in FIG. 3A, leads for a pluralityof light-emitting devices are actually connected to the main frame (notshown) through the tie bars 44.

As shown in FIG. 3B, the first resin 5 is then molded onto the leadframe by, for example, insert molding. The first resin 5 is formed ofoptically transparent resin; a highly heat-resistant transparent resinobtained by including glass components in, for example, Nylon (aregistered trademark) can be used as the first resin 5. The leads 41, 42and 43 are formed integrally with the first resin 5 such that parts ofthe upper surfaces thereof are held exposed from the first resin 5. Thefirst resin 5 is integrally molded such that side walls 51 higher thanthe upper surfaces of the leads 41, 42 and 43 are formed along the outercircumference of the upper surface of the first resin 5. The side walls51 have the function of appropriately forming the appearance shape ofthe second resin 7 when it is molded. In this way, a rein-frame typepackage 2 is formed with the lead frame.

As shown in FIG. 3C, the light-emitting elements 3 are then fixed ontothe upper surface of the lead 42 with adhesive material. In thisembodiment, the light-emitting elements 3 are used in which both theirpositive and negative electrodes are arranged on their upper surfaces.Thus, the backs of the light-emitting elements 3 are fixed onto the leadwith insulating adhesive material. After the light-emitting elements 3are fixed, the light-emitting elements 3 are electrically connected. Inthis embodiment, ones of the positive and negative electrodes of thelight-emitting elements 3 are connected, by the bonding wires 6, to thelead 42, on which the light-emitting elements 3 are fixed; the others ofthe positive and negative electrodes of the light-emitting elements 3are connected, by the bonding wires 6, to the leads 41 and 43 other thanthe lead 42, on which the light-emitting elements 3 are fixed.

Then, as shown in FIG. 3D, the light-emitting elements 3 and the bondingwires 6 are sealed together with the second resin 7. An opticallytransparent resin or an epoxy resin can be used as the second resin 7.Since the second resin 7 is arranged to come into contact with the firstresin 5, in order to prevent the first resin 5 from melting anddeforming when the second resin 7 is molded, a resin whose curingtemperature is less than the upper temperature limit of the first resin5 is used as the second resin 7. Although an optically transparent resinor an epoxy resin can be used alone as the second resin 7, in thisembodiment, a resin is used that contains a fluorescent material (notshown) varying the wavelength of light emitted from the light-emittingelement 3 and emitting it. In a case where a light-emitting element thatemits blue light is used as the light-emitting element 3, when afluorescent material is used that receives the blue light and emitsyellowish light, whitish light (including white light) is extracted as aresult of both the light being mixed. When a fluorescent material isused that can emit light having a large number of reddish components, itis possible to emit light having a number of reddish components likelight of daylight color (color of light emitted from a light bulb).

As a fluorescent material is arranged further away from thelight-emitting elements 3, it becomes less likely that the fluorescentmaterial is excited by light emitted from the light-emitting elements 3.This causes inconsistencies in color, and thus the fluorescent materialis preferably concentrated and arranged near the light-emitting elementsso that inconsistencies in color are prevented. For example, by using afluorescent material having a larger specific gravity than that of thesecond resin 7, it is possible to deposit the fluorescent material onthe bottom of the second resin 7 and thus concentrate and arrange thefluorescent material near the light-emitting elements 3.

The second resin 7 and the first resin 5 are molded separately asdescribed above, and this eliminates the need to take into accountwhether or not the first resin 5 is suitable for the fluorescentmaterial when the resin and material are selected. Thus, when the resinand material are selected, it is less likely to undergo restrictionsfrom the first resin 5. This helps design the arrangement of thefluorescent material in an optimum position.

As shown in FIG. 2, the second resin 7 is filled to the top of the frameformed by the side walls 51 of the first resin 5. Alternatively, it ispossible to place the second resin 7 only in the vicinity of thelight-emitting elements 3 such that the second resin 7 covers thelight-emitting elements 3.

After the second resin 7 is cured, the leads 41 and 43 are cut such thatportions serving as outer lead portions 41 a and 43 a used for externalconnection are left, and the tie bars 44 are cut near the side walls 51.Thus, the light-emitting devices 1 are individually completed by beingseparated from the lead frame.

In the light-emitting device 1 thus completed, when a predeterminedvoltage is applied between the outer lead portions 41 a and 43 aprotruding sideways from the side walls 51 of the first resin 5, apredetermined current is fed to the light-emitting elements 3, and thisallows them to be turned on. Part of light emitted from thelight-emitting element 3 excites the fluorescent material. As shown byarrows of FIG. 2, light emanating from the fluorescent material and thelight emitted from the light-emitting element 3 are directed to theupper surface of the device but part thereof is directed through theoptically transparent first resin 5 and the second resin 7 to the backside of the leads 41, 42 and 43. In this way, light is also extractedfrom the back side of the light-emitting device. Here, in order todirect a larger amount of light to the back side of the leads 41, 42 and43, it is preferable to mold the first resin 5 such that it covers moreof the backs of the leads 41, 42 and 43. Thus, in order to prevent thebacks of the leads 41, 42 and 43 from being exposed, it is preferable tocover the entire backs with the first resin in the light-emitting device1. In this way, it is possible to increase the amount of light extractedfrom the backs. This is preferable so that wide directivity is achieved.

FIGS. 4A and 4B show the distributions of the relative outputs oflight-emitting devices in upward, downward, leftward and rightwarddirections. As shown in FIG. 2, an angle of 0° (360°) indicates theleftward direction with respect to the device 1, an angle of 90°indicates the upward (frontward) direction with respect to the device 1,an angle of 180° indicates the rightward direction with respect to thedevice 1 and an angle of 270° indicates the downward (backward)direction with respect to the device 1. FIG. 4A shows the distributionof the relative output in the above-described embodiment; FIG. 4B showsthe distribution of the relative output in an example of a conventionallight-emitting device where an optically reflective white resin is usedas the first resin. A comparison of the above-described embodiment andthe example of the conventional light-emitting device with reference toFIGS. 4A and 4B shows that the relative amount of light in the directionof an angle of 270° (in the backward direction) is significantlyincreased from 0.1 in the case of the example of the conventional one to0.4 in the case of the above-described embodiment. Thus, according tothe above-described embodiment, it is possible to emit light in alldirections instead of one direction. This makes it possible to achievewide directivity.

FIGS. 5 and 6 show different embodiments of the present invention. Theseembodiments differ from the previously described embodiment in that theside surfaces 52 of the first resin 5 located on the left and rightsides of the light-emitting elements are designed such that the middleportions thereof in an up/down direction extend outward and that theupper outside surfaces of the side walls 51 extend outward in left andright directions as they extend from top and bottom.

In the embodiment shown in FIG. 5, when the side surfaces 52 of thefirst resin 5 are designed such that the middle portions thereof in anup/down direction extend outward, they are designed such that theoutlines of top, middle and bottom portions 52 a, 52 b and 52 c arecomposed of connected straight lines. In the embodiment shown in FIG. 6,when the side surfaces 52 of the first resin 5 are designed such thatthe middle portions thereof in an up/down direction extend outward, theyare designed such that the outlines of the top, middle and bottomportions 52 a, 52 b and 52 c are composed of connected arc-shapedcurves.

As described above, the side surfaces are designed such that the middleportions thereof in an up/down direction extend outward, and thus, byadjusting the critical angle of outgoing light from the side surfaces,it is possible to effectively guide, toward the backs, light that passesthrough the side surfaces and emanates sideways. This makes it possibleto increase the relative amount of light directed toward the backs. Thelight from the light-emitting device 1 is guided not only toward thebacks of the leads 41, 42 and 43 but also toward the outer lead portions41 a and 43 a through the first and second resins 5 and 7.

The light-emitting device 1 described above can be used as a lightsource that serves as the filament of a light bulb and that is anexample of a lighting apparatus.

FIG. 7 shows a front view of an LED (light-emitting diode) light bulbthat uses the above-described light-emitting devices as a filament andthat is an example of a lighting apparatus, with some parts omitted.With reference to FIG. 7, a description will be given of an LED lightbulb 8, that is, a lighting apparatus according to an embodiment of thepresent invention.

The LED light bulb 8 includes, in its base 10 hermetically sealing theopening of a glass cover 12, a control board (not shown) that convertscommercial electric power into electric power for driving the LEDs. Afilament 9 is firmly attached to a pair of power supply leads 11extending from the control board. The internal space of the light bulb 8is filled with an inert gas such as nitrogen, which excludes oxygen.

The filament 9 is formed with a plurality of the light-emitting devices1. In this embodiment, adjacent ones of the outer lead portions 41 a and43 a are firmly attached to each other by welding such that the six ofthe light-emitting devices 1 are connected in series. Both ends of acomponent obtained by connecting the light-emitting devices 1 in seriesare firmly attached by welding to the pair of power supply leads 11. Apair of the light-emitting devices 1 connected to the pair of powersupply leads 11 are arranged in parallel; the other light-emittingdevices 1 other than them are arranged such that adjacent ones of thelight-emitting devices 1 are V-shaped, that is, zigzag-shaped.

When the light bulb 8 configured as described above is fitted into anunillustrated socket, commercial electric power is applied to the base10, the integral control board performs power conversion and thus apredetermined direct current is fed to the leads 11. The predetermineddirect current is fed to the filament 9 through the leads 11, and thusthe predetermined current is passed through the individuallight-emitting devices 1 of the filament 9. In the light-emittingdevices 1, the light-emitting elements 3 emit light as a result of thepredetermined current being fed, and the emitted light passes throughthe resins 5 and 7 to illuminate the surrounding area. Since, asdescribed above, bar-shaped light-emitting devices 1 are arranged in azigzag manner and thus the filament 9 is shaped similar to a metalfilament, it is possible to take the same form of light emission as acommon incandescent light bulb. Specifically, for example, when aplurality of light-emitting diodes are fitted directly to the controlboard, interception of light by the control board or the like results innarrow directivity; however, with the lighting apparatus of thisembodiment, it is possible to achieve wide directivity as in anincandescent light bulb incorporating a metal filament.

Since the light-emitting devices 1 themselves have such wide directivitythat they can emit light in all directions, it is possible to increasethe degree of freedom to arrange the light-emitting devices 1 when theouter lead portion 41 a of the light-emitting device 1 is firmlyattached such as by welding to the outer lead portion 43 a of theadjacent light-emitting device 1. Moreover, since light can also beextracted from both the left and right ends of the light-emitting device1, more light can be guided toward the top of the cover 12 located onthe opposite side from the base 10 of the light bulb 8. Here, atransparent glass cover may be used as the glass cover 12 or a glasscover whose inner surface is subjected to light-scattering treatment andwhose color is of milky white may be used as the glass cover 12.

The present invention is not limited to the above embodiments. Manymodifications and variations are possible without departing from thespirit of the invention.

The present invention can be applied to a light-emitting device foremitting light from a light-emitting element over a wide area and to alighting apparatus incorporating such a light-emitting device.

1. A light-emitting device comprising: an elongated bar-shaped packageextending sideways, the package being formed such that a plurality ofleads are formed integrally with a first resin with part of the leadsexposed; a light-emitting element that is fixed onto at least one of theleads and that is electrically connected to at least one of the leads;and a second resin sealing the light-emitting element, wherein the firstresin and the second resin are formed of optically transparent resin,and the leads have outer lead portions used for external connection andprotruding sideways from both left and right ends of the package.
 2. Thelight-emitting device of claim 1, wherein the second resin includesfluorescent material.
 3. A lighting apparatus comprising: a plurality oflight-emitting devices that are provided as the light-emitting device ofclaim 1; a filament including the light-emitting devices; and powersupply leads electrically connected to the filament, wherein thefilament is so configured that adjacent ones of outer lead portions arefirmly attached and connected in series such that adjacent ones of thelight-emitting devices are V-shaped, and both ends of the outer leadportions connected in series are firmly attached to the power supplyleads.